The present invention relates to an optical memory in which data may be stored and reproduced by exposure to light.
Optical memories, such as optical discs, having a layer or film of semiconductor material, are widely used in industrial and consumer recording systems such as video recorders, digital audio recorders and document digital recorders. A signal is recorded on the optical memory by irradiation with a laser beam thereby forming bits of data in a layer of semiconductor material. The optical memory permits direct reading after the data has been written and random access to the recorded data.
Generally, it is known that a layer of semiconductor material, such as Te, has sufficient write sensitivity, even when recorded with a low-output laser beam. This element, however, is easily oxidized at a high humidity. For this reason, a protective film such as SiO.sub.2 is deposited on the surface, which in turn, causes degradation in write sensitivity.
An an example of an optical memory having improved write sensitivity is reported by C. R. Davis et al, "Proceedings SPIE, 420, 260 (1983)". This optical memory comprises an under layer, such as a plasma polymerized film having fluorine (F) and carbon (C), and a recording layer deposited on the under layer. The recording layer includes Te. This recording layer, however, cracks when subjected to an accelerated aging test. Therefore, in practice, this layer has not been used as the recording layer of an optical memory.
Moreover, M. Mashita and N. Yasuda disclose a recording layer containing a Te film having carbon (C) and hydrogen (H) (to be referred to as a Te-C film hereinafter ) in "Proceedings SPIE, 329, 190, (1982)". This Te--C film has a structure in which Te clusters are dispersed in a C--H matrix. This Te--C film is excellent in oxidation resistance, and preserves the high write sensitivity of a Te film without using a protective film. This film, however, is oxidized by H.sub.2 O and O.sub.2 diffused through the organic resin substrate such as the polycarbonate (PC), commonly used in optical memory systems, when exposed to high humidity over a long time period.